1. Field of the Invention
This invention relates to a microstrip antenna, and more particularly, to a dual-notch loaded microstrip antenna for dual-band or multi-band applications, wherein the dual-notch loaded microstrip antenna of the invention.
2. Description of Related Art
The dual-band signal-layer microstrip antenna has been widely used in applications like radar and communication systems, because of its advantages over a conventional antenna, such as lighter weight, lower profile and lower cost.
Generally, dual-band single-layer microstrip antennas can be categorized into categories include stub-type microstrip antenna, notch-type microstrip antenna, pin-and-capacitor-type microstrip antenna, and slot-loaded-type microstrip antenna.
As referring to FIG. 1, the top view of a conventional slot-type microstrip antenna disclosed in the U.S. Pat. No. 4,692,769, "Dual-band Slotted Microstrip Antenna", is shown. The slot-type microstrip antenna in FIG. 1 contains a slot 44, which stimulates the signals of some lower orthogonal modes and then emits the signals to achieve the dual-band function. Due to the slot and feeding structure shown in FIG. 1, two orthogonal lower-mode emissions are created, and the polarization direction of the antenna is 90 degrees.
Referring to FIGS. 2A and 2B, the top view and cross-sectional view of a conventional multi-band microstrip antenna are illustrated respectively, wherein the multi-band microstrip antenna has been disclosed in U.S. Pat. No. 5,329,378, "Multi-band Microstrip Antenna". For such a microstrip antenna, the achievement of emitting multi-band signals is carried out by partially hollowing out cavities in the single-layer substrate, or assembling cut media of different properties into a single layer substrate. However, not only the complicated fabrication process itself increases the fabrication cost, any minor misplacement of parts in assembly process or misalignment occurring in cutting process would seriously degrade the performance of the antenna.
Referring to FIGS. 3A and 3B, the top view and cross-sectional view of a multilayer dual-band microstrip antenna are illustrated respectively, wherein the multilayer dual-band microstrip antenna has been disclosed in U.S. Pat. No. 5,561,435 "Planar Lower Cost Multilayer Dual-band Microstrip Antenna". The dual-band microstrip antenna shown in FIGS. 3A and 3B consists of two stacked substrates, each of them contains a metal layer of various dimension. The dimensions of metal layers over substrates are defined correspondingly to the designated resonant frequencies. However, since the fabrication process of the foregoing dual-band microstrip antenna involves stacking two substrates, therefore, the fabrication cost is increased. In addition, shifting and defective coupling occurring in the stacking process also badly affect the performance and stability of the antenna.
In accordance with the foregoing, a microstrip antenna fabricated through a low-cost, efficient, and high-tolerance fabrication process is needed.